1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to a system and a method for streaming at least one content stream having a reduced access time for each content stream.
2. Description of the Related Art
An increasing number of disk-based storage systems are used for streaming content, in particular, video data. In such an environment, it is critical that the streams be maintained without any delays that would distort a delivered image. To do this, streaming-content disk drives are usually customized to have slower, more reliable servo systems in order to reduce seek errors. Additionally, the lowest possible RPM spindle speed is used in order to minimize acoustic problems and in order to provide the highest reliability possible for rugged environments in which such systems can be placed.
Many disk-based streaming-content storage systems stream multiple streams simultaneously. Accordingly, it is important for the hardware of such systems to provide the maximum performance in terms of the number of content streams that can be produced. A factor for providing maximum performance in terms of the number of content streams is the reducing the time for accessing a block of data in a disk-based streaming-content storage system. The time to access a block of data in a disk drive is includes the seek latency, the rotation latency for the data to arrive under the disk head, and the data transfer time.
The data in disk-based streaming content systems is typically read or written in data blocks of 128 KB or similarly sized blocks. Using the access times for an exemplary 5400 RPM Seagate Barracuda disk drive and data blocks of 128 KB, the worst-case total access time to read or write a video data block that has been randomly allocated on the Barracuda disk drive is the sum of the worst-case seek latency of 20 ms, the worst-case rotation latency of 11 ms and a data transfer time of 2 ms for a total worst-case access time of 33 ms. When the exemplary Barracuda disk drive is capable of out-of-order read, then worst-case total access time becomes the sum of the worst-case seek latency of 20 ms, the worst-case rotation latency of 11 ms and a data transfer of 0 ms (the data transfer occurs during the rotation latency) for a total worst-case access time of 31 ms. In either scenario, greater than 60% of the access time is caused by the seek latency.
Consequently, what is needed is a technique for reducing the time to access a block of data in a disk-based streaming-content storage system.